Radiogenic isotope evidence for cold spells in southern Greenland during the warm mid-Pliocene
Bibliographic record
Abstract
The warm mid-Pliocene (3.25-3.05 Ma) was the last time when Earth was warmer for a period longer than any Quaternary interglacial. According to recent studies, it was characterized by an atmospheric pCO 2 concentration close to 400 ppV and a mean global temperature about 3C above the recent pre-industrial temperature. Most data published so far point to a later onset of the Northern Hemisphere Glaciation, at ~ 2.6 Ma, when carbon dioxide concentrations reached values as low as ~ 280 ppm. In the present study, we use the IODP site U1307 record to document changes in marine sediment sources during the mid-Pliocene. Site U1307 was drilled 200 km south of Greenland (5830'N, 4624'W, 2575 m water depth) and should thus provide direct information on erosional regimes inland during this critical interval. Sediment samples were collected with a time-resolution of ~ 10 ka over the ~ 3.2 to 2.9 Ma sequence. Grain size and mineralogical analyses were completed by radiogenic isotope measurements (Nd, Pb) on the sediment fraction <64 m. Aside a few intervals with ice rafted debris (IRD, >150m), Nd isotopes depict a general trend towards more radiogenic sources from the mid-Atlantic ridge ridge/Iceland area, which we associated with a strengthening of the Atlantic Meridional Overturning Circulation (AMOC). Over this trend, isotopic excursions with ENd values below -20 point to intervals with enhanced supplies from the unradiogenic bedrock of southern Greenland, with a mean 45 ka pacing, which we associate to ice advances. Subsequent intervals with relatively high IRD contents would support this interpretation. These findings first suggest that despite the relatively warm global conditions of the interval, the AMOC intensified, whereas ice was at least sporadically present over part of southern Greenland, prior to 2.6 Ma, in agreement with recent propositions [1].
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".